1. Field of the Invention
This invention relates to automatically calibrating an electronic compass in a vehicle, especially an automotive vehicle. The invention eliminates the need for an intervention by the operator of the vehicle in the calibration process. Thus the calibration is done automatically thereby reducing chances for error and providing a more accurate calibration on a continuous or periodic basis without the intervention of the operator of the vehicle.
2. Description of Related Art
The subject invention is closely related to and is an improvement to the system described in commonly assigned U.S. Pat. No. 4,622,843 to Hormel on Nov. 18, 1986 and two other commonly assigned U.S. patent applications, U.S. Ser. No. 06/814,125 (now U.S. Pat. No. 4,677,754; 07/07/87), "The Multiplexing Of A Bandpass Filter Circuit To Work With A Flux-Gate Sensor Output" also to Hormel, and U.S. Ser. No. 06/814,133, now U.S. Pat. No. 4,750,349; 6/14/88, "Microcomputer Controlled Quick Ranging Technique And Digital Filter" to Luitje. All three of these documents were filed in the U.S. Patent & Trademark Office on Dec. 27, 1985 and the entire contents of these three documents are hereby expressly incorporated by reference.
More specifically, the subject invention is an improvement to the calibration method claimed in co-pending, commonly assigned U.S. Ser. No. 06/931,766, now U.S. Pat. No. 4,720,992; 1/26/88, "Calibration Sequence And Method For An Electronic Compass," filed on Nov. 17, 1986, which is also hereby expressly incorporated by reference.
Attention is invited to the Ser. No. 06/931,766 application. There, a calibration sequence and method is disclosed and claimed for use with an electronic compass. The sequence and method allows for the separation of the vehicle's magnetic field from the earth's magnetic field so that the earth's field can be measured and used to indicate vehicle direction; such calibration sequence being done with a mirrored 180 degree reorientation of the vehicle. See FIG. 3 herein for an illustration.
Other related art to the invention is contained in the following publications: "Magnetic Field Sensor And Its Application To Automobiles," SAE Paper No. 800123, pages 83 through 90, February 1980 by Hisatsugu Itoh; and "A Magnetic Heading Reference For The Electro/Fluidic Auto Pilot,"Sport Aviation, by Doug Garner, Part I, pages 19 through 26, November 1981 and Part II, pages 20-32 and page 51 in the December 1981 issue. Both of these documents are also hereby expressly incorporated by reference.
Other patents found by applicant or by the examiners in these commonly assigned patent and applications are listed in applicant's information disclosure statement. The relevance of these documents are dealt with in the respective files.